1. Field of the Invention
The present invention relates to equipment cases, wrist watch cases, and radio controlled watches.
2. Description of the Related Art
In the conventional art a radio controlled watch is known in which, for example, an antenna for receiving standard time radio waves is housed. The radio controlled watch corrects its time based on the standard time radio waves received by the antenna.
In timepieces such as the radio controlled watch above, when both the case body and the back cover (lid) are formed of metal, eddy current flux can be generated between the case body and the back cover. When this occurs, the signal receiving sensitivity of the antenna is lowered.
Accordingly, as a technology to solve this problem, in U.S. Pat. No. 7,126,548 and Japanese Patent Application KOKAI Publication No. 2006-112866, the installation of a spacer member between the metal case body and the metal back cover is described. As a result of this technology, current flux between the case body and the back cover is suppressed by the spacer member, thereby suppressing the lowering of the signal receiving sensitivity of the antenna.
However, when the back cover is fixed to the case body with the interposing spacer members via press fitting or screws, the securing force of the back cover is often weakened. When this occurs, high water resistance, for example, cannot be obtained.
In addition, a technology for strengthening the securing force of the back cover and additionally suppressing in part eddy current is described in U.S. Patent Application Publication No. 2006/0109188. In this technology, screw members are formed respectively on a portion of the periphery of the metal back cover and a portion of the inner surface of the metal case body. By threading and screwing these screw members together, the back cover is attached to the case body. Furthermore, the screw heads of the screw members formed on the case body are partially cut. As a result of this configuration, the technology described in U.S. Patent Application Publication No. 2006/0109188 reduces the surface contact area between the case body and the back cover, and partially suppresses eddy current.
However, in the technology described in U.S. Patent Application Publication No. 2006/0109188, although eddy current is suppressed, the more the screw heads are cut, the more the back cover securing force weakens.